Untersuchung dynamsicher Prozesse bei der Molekularstrahlepitaxie auf Silizium

Kästner, M.

Book/Report

FZJ-2019-04542

Untersuchung dynamsicher Prozesse bei der Molekularstrahlepitaxie auf Silizium

Kästner, M. (Corresponding author)FZJ*

1998
Forschungszentrum Jülich, Zentralbibliothek, Verlag Jülich

Jülich : Forschungszentrum Jülich, Zentralbibliothek, Verlag, Berichte des Forschungszentrums Jülich 3599, VIII, 139 p. (1998)

Please use a persistent id in citations: http://hdl.handle.net/2128/22639

Report No.: Juel-3599

Abstract: Dynarnical processes in thin film growth using molecular beam epitaxy (MBE) are studied with a recently developed experimental technique called $\textit{in vivo}$ scanning tunneling microscopy ($\textit{in vivo}$ ST112). With this method, it is possible to follow the evolution of specific features during growth. Homoepitaxial growth on Si(111) and heteroepitxial growth of Ge/Si(001) are investigated. In addition, the shadow of the STM tip is used to study the edges of shaded areas in MBE. The island size distribution after submonolayer deposition of Si on Si(111) exhibits pronounced peaks of magic sizes. lt is possible to study directly the influence of surface reconstruction on growth kinetics by in vivo STM. Lateral growth of rows of the width of the 7x7 reconstruction unit cell leads to kinetic stabilizatiori of magie islands. Kinetic Monte Carlo simulations are performed that reproduce the main experimental results and make it possible to estimate important energy barriers. The influence of elastic stress was exarnined in Ge/Si growth. The Stranski Krastanov wetting layer of Ge/Si(001) exhibits a 2 x N reconstruction. For coverages from 0.8 ML to 2 ML the value of N decreases from 16 to 8. The 2 x N reconstruction below 1 ML and its evolution in time give evidente for intermixing of Ge and Si.Above 2 ML threedimensional Ge islands with {105} facets known as hut clusters are observed. The evolution of size and shape of individual hut clusters is followed by in vivo STM. A slower growth rate is observed when an island grows to larger sizes. This behaviour can be explained by self-limiting growth. A kinetic growth model involving a nucleation barrier for each repeated growth of a new atomic layer on the {105} facets agrees with the experimental results for the evolution of the island volume. The experimentally observed transition from nearly square shaped islands to elongated islands is described by the kinetic growth model. For Ge/Si(111) the decay of twodimensional islands is monitored after the evaporation was terminated. Islands which are two monolayers high decay faster than islands which are one layer high. Thermodynamically stable twodimensional islands are not observed. lt is found that the stable structures are threedimensional islands probably relaxed by misfit dislocations. When a molecular beam is directed from the side towards the Si sample while the STM tip is stationary and dose to the sample surface, the tip shades pari of the sample surface. The edge of the shadow can be studied by STM imaging after the evaporation. A sharp edge isfound upon deposition of Si or Ge, but a smooth edge is observed for Sb. Two facts might explain this difference: first, the bonding of Sb to the Si substrate is much stronger than the bonding beteween successive layers of Sb, second, the Sb beam consists of quadrumeres rather than single atoms. Kinetic Monte Carlo simulations show that strong bonding to the substrate is essential for a smooth transition, while possible diffusion of quadrumeres with finite lifetime is not.

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